Fluid trap



M. NICOLAS Aprn 25, 1967 FLUID TRAP Filed Nov. 5, 1964 United States Patent O 3,315,448 FLUID TRAP Michel Nicolas, Bievres, France, assignor to Compagnie Industrielle Francaise des Tubes Electroniques Courbevoie, Seine, France Filed Nov. 5, 1964, Ser. No. 409,195 Claims priority, application France, Nov. 8, 1963, 953,127, Patent 1,387,101 6 Claims. (Cl. 55-441) This invention relates to a device adapted, in vacuum pumps operating according to the oil-vapor diffusion principle, to avoid any loss of oil as currently observed in conventional pumps of this type when air has accidentatlly been allowed to penetrate into .the circuit to be vacuumized. In fact, this ingress of air is attended, in said pumps, due to the physical mechanisms to be explained presently, by the transfer of a certain quantity of oil constituting the charge of these pumps When this transfer is repeated a number of times it reduces the oil charge of diffusion pumps to a volume inferior to that necessary for properly operating these pumps.

These disturbances are particularly detrimental in any industry requiring the use of extremely high pumping rates for obvious reasons of cost reduction. In fact, these pumping yoperations are usually carried out on automatic units comprising rotary turrets equipped with a relatively great number of working stations of which the vacuum circuit comprises in most instances an oil-vapor diffusion pump; under these conditions it is clear that a primary requirement of these production arrangements is to avoid as much as possible any interference or disturbance in the pumping operations, notably on account of oil losses, as explained hereinabove, which lead to frequent inspections or overhaulings of these pumping units at the expenses of production, although oil diffusion pumps equipping these units are unavoidably subjected to the ingress of air. This ingress of air is observed either compulsorily when fitting on each station of a pumping unit, at each cycle of rotation thereof, a fresh enclosure to be vacuumized, -or accidentally in case of breakage or leakage of an enclosure during the pumping operation; in the first case the air contained in the enclosure to he vacuumized is expanded: the ingress of air is sudden but short; in the second case the air circulation resulting from the accident may be either of short duration or relatively long; it is short if the unit is equipped with a safety device operating according to the leakage detection principle, or otherwise of relatively long duration, until the leakage is detected through any other means and the disturbing enclosure removed from the unit.

In each one of the cases contemplated hereinabove the oil transfer process is as follows:

When the air filling the volume to be vacuumized expands, the air stream fiowing through the pump destroys the normally constituted vapor sheets, thus carrying away said vapor at high speed towards the primary duct, then towards .the primary pump proper; the vapor obviously -condenses on the various walls and surfaces encountered along its path, but is lost as far as the diffusion pump is concerned. Now the oil charge of small-sized pumps designed for pumping units constitutes a relatively small volume (for example of the order of 0.5 to 0.9 cu. in. according to types); under these conditions, this charge is rapidly exhausted.

When air circulates due to a breakage or a clean crack, the air stream is considerably more important. Two phenomena take place: First, the vapor is carried away as in the above-mentioned case, then one fraction of this air is adsonbed by the oil which has thus been cooled.

3,315,448 Patented Apr. 25, 1967 When the air stream is disontinued (due to the repairing of the vacuum circuit) the pump will rapidly attain a pressure of -a few millimeters Hg, at which pressure the oil releases the previously adsorbed air. This desorption is always very strong and attended by an emulsion building up within the pump body in the form of a foam subsequently carried along into the primary duct. It is clear that after about ten accidents of this type the oi'l charge of the pump is reduced to a volume lower than the limit volume necessary for permitting its proper operation; under these conditions, the corresponding working station must be held up until the unit is overhauled; thus, in either case fa considerable production loss 1s experienced. y

It is the essential object of this invention to provide a device adapted to avoid the inconveniences broadly set forth hereinabove.

This device is adapted to retard the flow of oil vapor and to condense this vapor, while retarding likewise the aforesaid emulsion, by resorting to a specific and adequate arrangement of the defiection walls and iiuid-ow orifices as set forth hereinafter, whereby the oil carried away is recovered nearly completely.

To this end there is intenposed, in the connecting nozzle sleading to the primary priming pump for maintaining the preliminary vacuum, a two-compartment trap device incorporating a central cavity formed with orifices and defiectionmembers so arranged as to provide in the path of the oil vapor carried along by the air stream towards the primary vacuum duct a series of baffles adapted to retard this vapor and cause same to be condensed before attaining the trap outlet, the thus con-v densed vapor returning to .the pump without causing any pressure drops likely to interfere with the proper operation of the diffusion pump.

Reference will now be made to the accompanying diagrammatic drawing of which the single ligure illustrates in axial section a typical form of embodiment of the invention.

This device comprises an external cavity 1 and an inner coaxial cavity 2, the input nozzle 3 causing the oil fiow, as well as the oil emulsion and oil vapor,v to be retarded by defiection on the wall of cavity 1 (cooled by a water circulation 4 illustrated herein in the form of a metal pipe 4 welded on the trap 1) and the output nozzle 5 has a portion projecting into the last baille of annular configuration formed at the tail end of cavity 2. Thus the trap 1 is divided into two compartments by an intermediate partition 7 which, for simplifying the construction, is an integral part of cavity 2 having at its upper end a collar portion 8 adapted to deflect obliquely the stream of air and vapor flowing towards said cooled wall of the outer cavity where thel Vapor is condensed, and at its lower end with a flange 9 forming a certain annular gap with said cavity.

In the first case contemplated hereinabove (expansion of the air contained in the volume to be Vacuumized) the vapor carried along by the air flux through the input nozzle 3 will first strike the wall of cavity 1, then surge into the orifices a formed in the inner cavity 2, before issuing through vent holes b formed at spaced angular intervals in the upper portion of the cylinder constituting this cavity, at the level of the deection cone of collar 8, while diffusing the stream of air and Vapor obliquely towards the cooled wall of cavity 1, thus causing the vapor to condense on this wall, the whirling motion thus produced being inasmuch pronounced as the air-vapor stream is stronger and, therefore, inasmuch loaded with oil vapor; the condensed oil flows through the orifices d and e and returns to the pump body. To prevent the fluid to be trapped from by-passing the traps, the diameters of orifices d and e are selected to be as small as possible while permitting the ow of oil therethrough. These diameters have been determined experimentally as a function of the above-mentioned requirements and also of the viscosity of the oil used in the pump; the applicant constructed devices according to this invention wherein these diameters are about 0.138 and 0.78", respectively, with so-called silicone uid oils Si 703 and 704, these devices proving entirely satisfactory in the operation of automatic pumping units used in the manufacture of electron vacuum tubes. However, the above figures are given by way of example only and should not be construed as limiting the present invention, even as far as said uids are concemed.

In the second case (air circulation due to an accidental breakage or a clean crack in an enclosure) firstly the above-described phenomenon appears, then, after the vacuum circuit has been restored in proper operating conditions and when the pressure in the pump body drops to a few millimeter Hg, the oil starts bubbling in the boiler. The foam thus developed fills the pump body, spreads at the outlet thereof into the primary vacuum duct, attains the space V1 at the input end of the device of this invention where it flows into space V2 through the annular gap formed between the case 1 and the annular fiange 9, the purpose of this annular gap being to retard the expansion of said foam through the device. However, the foam will fill up the space V2 from which, if necessary, it can iiow through the orifices a into the central cavity constituting a third space V3. The dimensions of theV aforesaid annular gap, of said spaces V2 and V3-as well as of the orifices a provided between these spaces have also been determined by the trial and error method so that under the less favorable conditions the foam produced in the circuit cannot flow as high as the vent holes b; thus, as already explained, the occluded air is released and the condensed oil resumes integrally the liquid phase whereby, from this moment on, the conditions prevailing in the preceding case are restored: in other words, the oil flows on the one hand through'the orifices d and e, and on the other hand along a notch f milled vertically in the annular flange 9, the purpose of this notch being to permit the free flow of oil from said space V2, with the consequence that the liquid ring sealing by surface tension the annular gap'941 is broken, so that the gaseous ow towards the Y primary pumpV can be resumed while the oil owing from the device returns to the normal evaporation cycle. It is only in case another important ingress of air takes place while a large quantity of oil is still retained in the trap that a moderate quantity of this oil could possibly escape through the primary pumping orifice 5. It was observed that after introducing air at the atmospheric pressure 50 times into a pipe having an inner diameter of about 0.08 and a length of about 2%", these introductions lasting ten seconds and being spaced one minute from each other, the oil consumption was only 0.15 cu. in. in a pump having a 0.9 cu. in. oil charge, that is, of the order of which is a remarkable improvement if compared with consumptions measured with pumps not equipped with this oil economizer, forthis device permits of effecting over- 6 hauls of the automatic pumping units which are as much as four to five times more spaced from one another in time, thus affording a considerable gain in maintenance and production. Y A

The notch f like the diameters of orifices a and bentY holes b are also calculated experimentally soA that the loss of pressure resulting therefrom as a whole cannot interfere with the proper operation of the device. Thus, by way of example, the semi-cylindrical sectioned notch f is 0.1575" wide and 0.08 deep; theV diameter of orifice a is 0.12", that of vent holes b is also 0.12", it being understood however that these dimensions are also given by way of example and should not be construed as limiting the present invention in any way.

Although the Ypresent invention has been described in conjunction with a preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

What I claim is:

1. A iiuid trap to separate any entrained liquid in a gas ow comprising a central cavity, two superposed annular compartments surrounding said central cavity, an input nozzle at the lower portion of the lower compartment, an output nozzle at the upper portion of the upper compartment, an annular partition 4separating said two superposed annular compartments, said central'cavity comprising Va first orifice located just beneath said annular partition, a second orifice at its upper portion, a third orifice just above said annular partition, and a fourth orifice in its bottom.

2. A fluid trap as set forth in claim 1, wherein said central cavity comprises externally, at its upper portion,

in said upper annular compartment, a deector adapted to direct downwards the gas issuing from said inner cavity through its second orifice.

3. A fluid trap as set forth in claim 2, wherein an annular fiange extending externally of the lower portion of said inner cavity determines the cross-sectional area of lthe input passage leading into said lower annular compartment.

4. A fluid trap as set forth in lclaim 3, wherein a vertical notch is formed in said annular flange.

5. A fluid trap as set forth in claim 1, wherein said input nozzle is slightly inclined upwards and inwards with respect to the horizontal and extends beyond the axis of the device, said output nozzle commencing in the vicinity of said axis.

6. A fluid trap as set forth in claim 1, wherein theV diameters of said third and fourth orifices of said central cavity are smaller than those of said first and second orifices.

References Cited by the Examinery UNITED STATES PATENTS 2,386,298 10/1945 Downing 230-101 2,714,484 8/1955 Carr 230-101 3,007,624 ll/ 1961 Netzel 230-45 FOREIGN PATENTS 765,978 4/1934 France. 748,376 5 1956 Great Britain.

V. EFNER, Primary Examiner, 

1. A FLUID TRAP TO SEPARATE ANY ENTRAINED LIQUID IN A GAS FLOW COMPRISING A CENTRAL CAVITY, TWO SUPERPOSED ANNULAR COMPARTMENT SURROUNDING SAID CENTRAL CAVITY, AN INPUT NOZZLE AT THE LOWER PORTION OF THE LOWER COMPARTMENT, AN OUTPUT NOZZLE AT THE UPPER PORTION OF THE UPPER COMPARTMENT, AN ANNULAR PARTITION SEPARATING SAID TWO SUPERPOSED 